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Date:   Sat, 28 May 2022 16:22:56 -0400
From:   Alan Stern <stern@rowland.harvard.edu>
To:     syzbot <syzbot+02b16343704b3af1667e@syzkaller.appspotmail.com>
Cc:     andreyknvl@gmail.com, gregkh@linuxfoundation.org,
        linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
        syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] WARNING in driver_unregister
Message-ID: <YpKEoBORZLtXG/y9@rowland.harvard.edu>
References: <YpJaiGRcRjDzRxQC@rowland.harvard.edu>
 <0000000000007a6b3605e01620c8@google.com>
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On Sat, May 28, 2022 at 10:55:22AM -0700, syzbot wrote:
> Hello,
> 
> syzbot has tested the proposed patch and the reproducer did not trigger any issue:
> 
> Reported-and-tested-by: syzbot+02b16343704b3af1667e@syzkaller.appspotmail.com
> 
> Tested on:
> 
> commit:         97fa5887 USB: new quirk for Dell Gen 2 devices
> git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
> kernel config:  https://syzkaller.appspot.com/x/.config?x=d7b232ec3adf5c8d
> dashboard link: https://syzkaller.appspot.com/bug?extid=02b16343704b3af1667e
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> patch:          https://syzkaller.appspot.com/x/patch.diff?x=10f44625f00000
> 
> Note: testing is done by a robot and is best-effort only.

Yeah, I don't believe this result.

In any case, I believe the second problem (unexpected unregistration) 
arises because the driver has no protection against multiple threads 
calling raw_ioctl_run() concurrently.  Fixing that should be a second 
patch, but for testing purposes the two are combined below.

Alan Stern

#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git 97fa5887cf28

Index: usb-devel/drivers/usb/gadget/legacy/raw_gadget.c
===================================================================
--- usb-devel.orig/drivers/usb/gadget/legacy/raw_gadget.c
+++ usb-devel/drivers/usb/gadget/legacy/raw_gadget.c
@@ -11,6 +11,7 @@
 #include <linux/ctype.h>
 #include <linux/debugfs.h>
 #include <linux/delay.h>
+#include <linux/idr.h>
 #include <linux/kref.h>
 #include <linux/miscdevice.h>
 #include <linux/module.h>
@@ -36,6 +37,9 @@ MODULE_LICENSE("GPL");
 
 /*----------------------------------------------------------------------*/
 
+static DEFINE_IDA(driver_id_numbers);
+#define DRIVER_DRIVER_NAME_LENGTH_MAX	32
+
 #define RAW_EVENT_QUEUE_SIZE	16
 
 struct raw_event_queue {
@@ -145,6 +149,7 @@ enum dev_state {
 	STATE_DEV_INVALID = 0,
 	STATE_DEV_OPENED,
 	STATE_DEV_INITIALIZED,
+	STATE_DEV_REGISTERING,
 	STATE_DEV_RUNNING,
 	STATE_DEV_CLOSED,
 	STATE_DEV_FAILED
@@ -160,6 +165,9 @@ struct raw_dev {
 	/* Reference to misc device: */
 	struct device			*dev;
 
+	/* Make driver names unique */
+	int				driver_id_number;
+
 	/* Protected by lock: */
 	enum dev_state			state;
 	bool				gadget_registered;
@@ -188,6 +196,7 @@ static struct raw_dev *dev_new(void)
 	spin_lock_init(&dev->lock);
 	init_completion(&dev->ep0_done);
 	raw_event_queue_init(&dev->queue);
+	dev->driver_id_number = -1;
 	return dev;
 }
 
@@ -198,6 +207,9 @@ static void dev_free(struct kref *kref)
 
 	kfree(dev->udc_name);
 	kfree(dev->driver.udc_name);
+	kfree(dev->driver.driver.name);
+	if (dev->driver_id_number >= 0)
+		ida_free(&driver_id_numbers, dev->driver_id_number);
 	if (dev->req) {
 		if (dev->ep0_urb_queued)
 			usb_ep_dequeue(dev->gadget->ep0, dev->req);
@@ -421,6 +433,7 @@ static int raw_ioctl_init(struct raw_dev
 	struct usb_raw_init arg;
 	char *udc_driver_name;
 	char *udc_device_name;
+	char *driver_driver_name;
 	unsigned long flags;
 
 	if (copy_from_user(&arg, (void __user *)value, sizeof(arg)))
@@ -439,36 +452,44 @@ static int raw_ioctl_init(struct raw_dev
 		return -EINVAL;
 	}
 
+	ret = ida_alloc(&driver_id_numbers, GFP_KERNEL);
+	if (ret < 0)
+		return ret;
+	dev->driver_id_number = ret;
+
+	driver_driver_name = kmalloc(DRIVER_DRIVER_NAME_LENGTH_MAX, GFP_KERNEL);
+	if (!driver_driver_name) {
+		ret = -ENOMEM;
+		goto out_free_driver_id_number;
+	}
+	snprintf(driver_driver_name, DRIVER_DRIVER_NAME_LENGTH_MAX,
+				DRIVER_NAME ".%d", dev->driver_id_number);
+
 	udc_driver_name = kmalloc(UDC_NAME_LENGTH_MAX, GFP_KERNEL);
-	if (!udc_driver_name)
-		return -ENOMEM;
+	if (!udc_driver_name) {
+		ret = -ENOMEM;
+		goto out_free_driver_driver_name;
+	}
 	ret = strscpy(udc_driver_name, &arg.driver_name[0],
 				UDC_NAME_LENGTH_MAX);
-	if (ret < 0) {
-		kfree(udc_driver_name);
-		return ret;
-	}
+	if (ret < 0)
+		goto out_free_udc_driver_name;
 	ret = 0;
 
 	udc_device_name = kmalloc(UDC_NAME_LENGTH_MAX, GFP_KERNEL);
 	if (!udc_device_name) {
-		kfree(udc_driver_name);
-		return -ENOMEM;
+		ret = -ENOMEM;
+		goto out_free_udc_driver_name;
 	}
 	ret = strscpy(udc_device_name, &arg.device_name[0],
 				UDC_NAME_LENGTH_MAX);
-	if (ret < 0) {
-		kfree(udc_driver_name);
-		kfree(udc_device_name);
-		return ret;
-	}
+	if (ret < 0)
+		goto out_free_udc_device_name;
 	ret = 0;
 
 	spin_lock_irqsave(&dev->lock, flags);
 	if (dev->state != STATE_DEV_OPENED) {
 		dev_dbg(dev->dev, "fail, device is not opened\n");
-		kfree(udc_driver_name);
-		kfree(udc_device_name);
 		ret = -EINVAL;
 		goto out_unlock;
 	}
@@ -483,14 +504,24 @@ static int raw_ioctl_init(struct raw_dev
 	dev->driver.suspend = gadget_suspend;
 	dev->driver.resume = gadget_resume;
 	dev->driver.reset = gadget_reset;
-	dev->driver.driver.name = DRIVER_NAME;
+	dev->driver.driver.name = driver_driver_name;
 	dev->driver.udc_name = udc_device_name;
 	dev->driver.match_existing_only = 1;
 
 	dev->state = STATE_DEV_INITIALIZED;
+	spin_unlock_irqrestore(&dev->lock, flags);
+	return ret;
 
 out_unlock:
 	spin_unlock_irqrestore(&dev->lock, flags);
+out_free_udc_device_name:
+	kfree(udc_device_name);
+out_free_udc_driver_name:
+	kfree(udc_driver_name);
+out_free_driver_driver_name:
+	kfree(driver_driver_name);
+out_free_driver_id_number:
+	ida_free(&driver_id_numbers, dev->driver_id_number);
 	return ret;
 }
 
@@ -508,6 +539,7 @@ static int raw_ioctl_run(struct raw_dev
 		ret = -EINVAL;
 		goto out_unlock;
 	}
+	dev->state = STATE_DEV_REGISTERING;
 	spin_unlock_irqrestore(&dev->lock, flags);
 
 	ret = usb_gadget_register_driver(&dev->driver);